Traditionally, raw tires formed by a molding machine are stored at room temperature on racks in a stockroom, with which a building or the like for a vulcanization installation is equipped. Thereafter, the raw tires thus stored are transported from the racks to a vulcanization machine in accordance with a predetermined production program. In the vulcanization machine, the raw tries are heated up at a vulcanization temperature, and then the vulcanization/molding of the tires is carried out. In this case, when the raw tires are stored at room temperature for a long time, the tires are cooled at a much lower temperature than the vulcanization starting temperature, for instance, at such a low temperature as 25° C. Accordingly, a longer time is normally required to completely vulcanize the raw tire after heating it at a temperature greater than the vulcanization starting temperature. In view of this fact, several methods for storing the raw tires are conventionally employed or envisaged: In one method, raw tires are stored in a stockroom, the environment of which is maintained at a preheating temperature near the vulcanization starting temperature; and in the other method, the raw tires are directly preheated by irradiating them with a microwave.
In the conventional method for preheating the raw tires by conditioning the stockroom at the preheating temperature, it is necessary to heat the overall stockroom at such a preheating temperature and to maintain it at the temperature. Furthermore, the preheating (heating) is carried out exclusively on the front surface side of the raw tires, whereas the heating is delayed in the inside, so that a sufficient preheating can be attained in the process of the vulcanization/molding. These facts may provide a possible problem in which the running cost is significantly increased.
In the method for irradiating the raw tire with a microwave, the overall raw tire is exposed to the microwave, so that it is difficult to uniformly preheat the raw tire in the direction of the tire width, when the raw tire has a complicated shape, varied thickness and complicated inner structure.
Accordingly, it is an object of the present invention to provide a method and an apparatus for preheating a raw tire, in which the preheating can be carried out uniformly over the entire tire at a decreased running cost.